PUB - Publikationen an der Universität Bielefeld

Pulsars are the most precise and stable macroscopic clocks in nature. With spinning periods of only a few milliseconds and timescales of the order of years, these astrophysical clocks can easily compete with the best atomic clocks on earth. The fast rotation of the pulsars induces through the lighthouse effect a radio beam that can cross the line of sight of earth and appears to us as periodic pulses. Using the technique of pulsar timing, which compares the measured times of arrivals against predictions from theoretical timing models, opens the door for testing gravitational physics in the strong gravity regime around these compact and dense objects. In this dissertation, based on gained timing data from observing campaigns with the Arecibo and Effelsberg telescopes, we will present an update to previous gravity test results from the pulsar-white dwarf binary PSR J1738+0333 . We confirm the validity of General Relativity and set tighter constraints on the parameter space of Scalar-Tensor gravity theories as the most promising candidates among many alternative gravity theories.

In addition, we investigate the possible detection of a pulsar orbiting in the vicinity of the supermassive black hole SgrA∗ . We approach this problem by deriving an analytical formula based on Einstein’s theory of General Relativity which predicts the propagation time delay in the Kerr space-time and deduces the frame dragging times delay associated with the spin of the black hole. Finally we compare our results with previous Post-Newtonian approximations. We also discuss the stability and the precision of our approach.